We shall determine the conformations of oxytocin in aqueous solution using NMR measurements on a number of appropriately isotopically substituted isomers of oxytocin. Coupling constants between various types of nuclei (1H, 13C, and 15N) will be determined, and torsion angle values will be deduced from the coupling constants. These values may be single (fixed) or they may be multiple indicating the occurrence of rotational isomers. Conformations of the oxytocin ring will be obtained from the experimental torsion angle values using computer assisted calculations. To the degree possible, similar conformational will be obtained about the tripeptide tail and the side chains. Suitable methods for the syntheses of the isoptopic isomers of oxytocin will be devised, and the isomers will be prepared. In general, each isomer will contain 4-8 residues modified by the incorporation of 1-4 atomic isotopes. We estimate than 20 oxytocin isomers will be required, which will incorporate a total of 50-60 amino acid isotopic isomers.